The invention concerns the field of determining the positions of mobile communication terminals within telecommunication installations.
In the present context the expression “telecommunication installation” means an installation including in particular at least one broadcast network, for example radio (and in particular digital radio), satellite or wide-band multimedia broadcast network, and/or a mobile telephone network. Furthermore, as used hereinafter, the expression “telecommunication network” means any type of network, of a telecommunication installation of the invention, capable of transmitting by means of waves (frames of) communication data, of whatever form.
The person skilled in the art knows that more and more mobile communication terminals are equipped with applications relying at least in part on the determination of their respective positions. Furthermore, more and more services offered by mobile telecommunication network operators to their customers possessing mobile terminals rely at least in part on knowing the positions of their mobile terminals.
Positions may be determined by two different techniques. A first technique consists in determining the position of the mobile signal by processing signals (multiple access phase-modulated CDMA or FDMA signals), and navigation data that they contain, supplied by at least four different satellites of a Global Navigation Satellite System (GNSS) type positioning network, such as the GPS network, for example, the GLONASS network, or the future GALILEO network. This first technique requires the mobile terminal whose position is to be determined to be fitted with a satellite positioning device.
The second technique consists in estimating the position of a mobile terminal in the base station systems (BSS) that certain cellular mobile telecommunication systems include, such as GSM/GPRS and UMTS networks. Simplifying, this estimation necessitates an exchange of paging messages between the mobile terminal and the BSS to enable determination of the cell in which the mobile terminal is situated, followed by determining its location within the cell by an analysis of the message propagation time.
The first technique offers a positioning accuracy of the order of around 50 to around 100 meters, which is incompatible with certain applications or certain services linked to the immediate environment of the mobile terminals. Moreover, this first method can be used only if the mobile terminal can simultaneously receive signals and acquire navigation data from at least four satellites. This condition is frequently not met, in particular in certain urban environments (known as “urban canyons”) and irregular environments such as mountainous areas, areas with a high density of tall buildings, tunnels, and indoor locations.
The second technique offers a positioning accuracy of the order of a few hundred to a few thousand meters, depending on the dimensions of the cells of the telecommunication network. It is therefore also incompatible with certain applications or certain services linked to the immediate environment of the mobile terminals.
In an attempt to improve on this situation, it has been proposed to combine the first method with another method, such as an inertial method, for example, or to combine navigation data from different positioning networks (including the LORAN C network). However, these combinations are costly and/or offer unsatisfactory positioning accuracy and/or cannot be used in urban canyon type environments and/or cannot function continuously and autonomously over large areas.